1. Field of the Invention
This invention relates to control for engine of the vehicles for agricultural work, especially agricultural tractors, equipped with rotary type working implement, such for cultivation, trench digging and so forth.
2. Description of the Prior Art
When rotary work implement is set to a vehicle for agricultural work, in order to perform cultivation, trench digging or the like, engine load will fluctuate according to the condition of the field, thus to increase when there locally is harder soil, causing the fear, in an extreme case, of the engine failure under too heavy loading. In such case, the engine overload should be released by raising the rotary working implement.
It indeed is conventionally known to provide automatic control for raising and lowering the rotary working implement in response to such field condition. According to such prior art, actual engine rotation of the agricultural work vehicle is sensed, and the so-sensed actual engine rotation is compared with a predetermined value. If the sensed actual rotation is lower than the predetermined desired value, then the rotary working implement is automatically raised; and if higher than desired, then the implement is automatically lowered; thus to maintain the engine rotation always near the set desired value. With such conventional control, the engine is indeed well maintained always near the desired rotation speed, thus without the fear of accidental failure of the engine.
However, such prior art has as its primary object only to maintain the predetermined engine rotation throughout the field operation, and has thus the drawbacks in that the working depth can not be kept constant, as it will heavily fluctuate when there are locations in the field where the soil is locally harder and softer. Fluctuation of the work depth will affect the yields of the crops, especially the effect is serious when the work is cultivation, namely when there is fluctuation in the cultivation depth, resulting in sharp decrease in the yields of the crops.